Spring In Action-3.2@Conditional条件化Bean

@Conditional
根据某个条件来决定是否创建Bean实例

代码下载地址：http://download.csdn.net/download/poiuy1991719/9965794

创建一个Bean类：

package com.bean.conditional;

import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Component;

@Component("magicBeanName")//重命名：配置类里面的方法与之对应
@Conditional(MagicCheck.class)//决定是否创建Bean的条件类
public class MagicBean {
    private String name="MagicBean";
    public MagicBean() {
        System.out.println("MagicBean:实例化");
    }
    
    public void showName(){
        System.out.println("Show Name is:"+name);
    }
}

创建一个Config配置类：配置类指定了一个Check类：

package com.bean.conditional;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan(basePackages={"com.bean"})
public class BeanConfigs {

    @Bean
    @Conditional(MagicCheck.class)//决定是否创建Bean对象
    public MagicBean magicBeanName(){//方法名来源，Bean类的注解：@Component("magicBeanName")
        return new MagicBean();
    }
}

Check类决定是否创建Bean的实例：Check类需是Condition类的一个实现：

package com.bean.conditional;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

//决定Bean的创建，需是Condition的一个接口
public class MagicCheck implements Condition {

    public boolean matches(ConditionContext arg0, AnnotatedTypeMetadata arg1) {
        return true;//创建Bean实例
//        return false;//不创建Bean实例
    }
}

测试类：

package test;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.bean.conditional.BeanConfigs;
import com.bean.conditional.MagicBean;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes={BeanConfigs.class})
public class test {
	@Autowired
	MagicBean mb;
	
	@Test
	public void selfTest(){
		if(mb==null){
			System.out.println("MagicCheck类决定了Bean的创建，MagicCheck类方法返回：false");
		}else{
			System.out.println("MagicCheck类决定了Bean的创建，MagicCheck类方法返回：true");
			mb.showName();
		}
	}
}